1. Field of the Invention
The present invention relates to means for determining the presence of a transparent liquid in a transparent angiographic syringe barrel and, more particularly, to means by which the presence of such a liquid is indicated by an alteration in the shape of an indicator pattern when viewed through the barrel.
2. Description of the Prior Art
One of the dangers involved in the injection of fluids into a patient is the risk that air will be accidentally injected into the patient. This danger is particularly acute in the case of angiographic equipment where blood vessels are sludied by using x-rays while injecting a contrast medium into the body through a catheter inserted in a blood vessel. The contrast medium is frequently colorless, and because such procedures are usually performed under relatively low light levels to facilitate reading of the x-rays, the ever-present danger is magnified. It is therefore highly desirable to provide a means whereby the presence of an empty or an only partially filled syringe can be readily detected prior to the attempted injection.
One approach to the problem of fluid presence detection is set forth in U.S. Pat. No. 4,006,736, issued on Feb. 8, 1977, to Kranys et al. That patent describes two different circuits for detecting the presence of air in a syringe cartridge by monitoring motor current or utilizing a characteristic of the syringe-fluid combination. Such systems are quite complicated and expensive.
U.S. Pat. No. 330,621, issued on Nov. 17, 1885, to Reichardt, shows, in a hypodermic syringe, a glass tube in which graduation lines on the back of the tube are magnified when viewed through a liquid to faciitate reading. In the absence of the liquid, the graduations are not magnified and do not appear as though extending entirely around the transparent tube. In this way the magnification of the graduations indicates the quantity of a liquid in the syringe.
U.S. Pat. No. 1,225,604, issued on May 8, 1917, to Ernst, relates to a sight gauge which includes a spaced member having vertical rows of circular holes which appear circular when the glass tube is empty, and appear transversely elongated when water is present in the glass.
While the foregoing prior art disclosures relating to fluid presence detection may be useful in the particular applications described therein, they are inadequate for syringes used in connection with angiographic injectors such as those described in U.S. Pat. No. 4,006,736. Such apparatus includes a syringe cartridge housed within a pressure jacket. The pressure jacket is generally of a clear polycarbohydrate material and the syringe is typically a polyethylene material which is also clear. However, in the low-light levels typically experienced during an angiographic scan, graduations and lines such a those described in the Reichardt patent are not readily distinguishable. Similarly, the circular openings described in the Ernst patent are not useful under those conditions because they depend upon the transmission of light through the back of the syringe from all directions. In contrast, angiographic injectors are typically used with the light being directed from above.
Accordingly, it is an object of the present invention to provide a means whereby the presence of an empty or an only partially filled syringe can be readily detected under lowlight levels prior to injection by direct visual means and without the use of electronic circuitry, backlighting or the like.